WO1991000152A1

WO1991000152A1 - Corrosion protective agent and a method for applying the same

Info

Publication number: WO1991000152A1
Application number: PCT/SE1990/000447
Authority: WO
Inventors: Bengt Jungqvist
Original assignee: Geveko Industri Ab
Priority date: 1989-06-26
Filing date: 1990-06-21
Publication date: 1991-01-10
Also published as: EP0480967A1; JPH04506368A; AU5934390A

Abstract

The present invention relates to a composition and an application method which prevents the occurrence of ''co-webbing'' when spraying an anticorrosive agent containing a thermoplastic polymer.

Description

Corrosion protective agent and a method for applying the same

The present invention relates to an anticorrosive agent and a method for the application thereof according to the preamble of the following patent claims 1-7.

Prior art and problem:

Anticorrosive treatments of different kinds have today become more and more important, especially within the car manufacturing. One known type of anticorrosive treatment is based on covering the surfaces that are to be protec¬ ted against corrosion with agents that at elevated tempe¬ ratures are liquid. This property allows the agent to be applied in a rational way, preferably by being sprayed. Such agents are often based on wax.

The disadvantage connected with such anticorrosive agents is that they give a very small or no protection against mechanical impact, which means that an anticorrosion treated part after having been damaged (for example by a stone shot) can be subjected to corrosive attacks.

To avoid the above-mentioned disadvantage one has looked for alternative agents which, besides having the ability of protecting against corrosion, also have a certain degree of wearing protection. PVC (polyvinyl chloride) and PU-based (polyurethane) agents have in this connec¬ tion been proved to fullfill this latter criterium. These agents are, however, from an environmental point of view not desirable and require in certain cases a non-conven- tional application equipment. Attempts have also been made with agents of the first mentioned type, for example wax-based, into which one has included additives to increase the wearing protection ability of the agent. Such an additive is thermoplastic rubber, which have rubber properties in temperatures somewhere under 100° and which have resin-like properties in temperatures somewhere above 100°. A thermoplastic rubber may consist of styrene-butadiene, styrene-isoprene or styrene.-ethylene/butylene-thermoplastics.

The above-mentioned polymers can chemically be described as polymers consisting of block segments of styrene mono¬ mers and rubber monomers (butadiene or isoprene and ethy- lene/butylene) . The polymers may exist as a diblock, a triblock or in branched (radial) structure.

Before heating, the polystyrene is associated in rigid segments. Physical cross binding creates via polystyrene segments a threedimensional net.

Under influence of heat and shearing forces the poly¬ styrene blocks are softened and the system becomes liquid. After cooling, the polystyrene blocks are rebuilded and locks the net bindings of the rubber part in place.

This physical cross-binding and reinforcement which is obtained through the polystyrene gives a high tensional strength whereas the rubber block provides high flexibi- lity.

Further, there are styrene- and olefine thermoplastics, which are segmencopolymers of styrene and mixtures of olefines, for example ethene, propene and/or butene. Attemps have, as mentioned, been made with anticorrosive agents containing thermoplastic rubber. It has then been desirable to be able to use the application equipment on hand, which often is an arrangement where the agent is sprayed on, and to be able to apply the agents without using non-desirable compounds from an environmental point of view, such as solvents. A problem one then has experi¬ enced is that the thermo-rubber already has been subjec¬ ted to a non-desirable, phase, tranafor ance before it has reached the surface that is to be anticorrosion treated. The phase transformance means that one gets a thread-like cover of the thermoplastic rubber, a so called "co-webbing" A treatment with an agent containing a thermoplastic rub¬ ber where "co-webbing" has occured, does not have the de- sired spray and anticorrosive properties.

To counteract the last problem, it has been proposed to connect hot air to the spray nozzle. The hot air arrange¬ ment is made in such a way that by application a hot air supply surrounding the spray jet in the shape of a cone is achieved. Due to this supply of hot air the "co-web¬ bing" is counteracted and an anticorrosive cover with the desired properties is obtained.

The last described method is, however, complicated and, consequently, also expensive. It does not only require complementary equipment but also a special "know-how", which also gives rise to non-desirable extra costs. If one by means of this method desires to accelerate the production, one has in proportion thereto to provide ne¬ cessary extra equipment. Every aggregate must then be handled in the prescribed way for obtaining the desired result. This requires extra education efforts and also control efforts which are directed to every single spray nozzle. This leads to increased complexity which is not desirable. Solution and advantages:

The object of the present invention is to obtain an anti¬ corrosive agent and an application method which elimina¬ tes the disadvantages which are connected with the above- mentioned known agents and application methods.

Said objects are attained by means of an anticorrosive agent according to the present invention which primarily relates to a composition intended to be applied on the surface by spraying of the hot liquid composition for obtaining a cover which is resistant to wear and corro¬ sion, the composition comprising a first glue-based bin¬ der, a second part of fillers and a third part consisting of a thero plastic polymer containing said thermoplastic rubber, and being characterized in that said second part of fillers contains compounds with a high heat capacity.

In the figures:

The invention shall be described in detail in the follow- ing by means of an embodiment example in connection to the attached drawings of which:

Fig. 1 schematically shows an application arrangement according to the invention,

Fig. 2 schematically shows an arrangement for performing a modified method according to the invention,

Fig. 3 shows in more detail a chosen part of Fig. 2, and

Fig. 4 shows an alternative modified method where the space is limited by the object that is to be cor¬ rosion-treated. Fig. 1 shows an object 1 with a surface 2 which is to be corrosion-treated. The schematically shown application arrangement comprises a container 3 which contains the liquid and the corrosive agent 4. The agent is kept li- quid by means of a suitable heat dissipating means 5 which, for example, by means of convection heat dissipa¬ ting means 6, releases a suitable (not shown controlling means) heat amount to the anticorrosive agent 4. Further, a spraying nozzle 7 is shown which sprays a fog 8 of the agent towards the surface 2 that is to be protected. Bet¬ ween the nozzle 7 and the container 3 there is a connec¬ ting pipe 9. To this pipe 9 is in a suitable way a pres¬ sure increasing aggregate 10 connected.

By means of the above schematically described arrangement it is possible to apply the anticorrosive agent in a li¬ quid state by spraying which means an approximate tempe¬ rature of about 150° C and an approximate pressure of 100 bar. Suitable limits for the temperature or the pressure respectively are 140-200° C and 50-200 bar.

The solution according to the invention is based on the application of a filler with high heat capacity to the anticorrosive agent. Due to the use of such a filler, the undesirable generation of "co-webbing" is counteracted. The reason hereto is that fillers carry a sufficiently great heat amount so that the thermoplastic rubber, which is included in the anticorrosive agent, is not cooled down to the critical "co-webbing" limit until it reaches the object 1 to be protected.

By the expression heat capacity is primarily meant the ability to store heat. As the weight of the agent is of minor importance, it is here primarily directed to the ability per volume unit, which means that an agent with a low specific heat and high density (for instance BaS0₄; 0,11 resp. 4,8) may as well be interesting as a compound with a high specific heat and lower density, (for example Al; 0,21 resp. 2,69). A table showing the product of spe¬ cific weight and specific heat for a number of different agents is shown in the following.

Specweight (at 15°C) Specheat (at 15°C) Product g/cm³ cal/g, °C cal/cm³,

To obtain a good result in accordance with the invention it has been shown that the filler should have a "product" which exceeds 0,32, preferably exceeding 0,5 cal/cm³, °C, and that the filler, when being sprayed on, is not in the state of vapour but preferably in a solid state.

Another factor which in some cases can be of some impor¬ tance, is that the filler has the ability to relatively quickly release its heat to the surrounding mass during the air travel from the nozzle to the surface which is to be protected. This means that the agent in some preferred cases also should have a relatively good heat contacting ability and/or a small grain size. A disadvantage with decreased grain size is, however, that the smallest pos¬ sible part of binder increases as the total exposed sur¬ face per volume unit is increased. Advantages and disad- vantages must, accordingly, be compared with each other for finding an optimum. The following table shows the grain size (in μm) of the fillers that have been used. Grain size of the different fillers

Aluminium Magnesium silicate Montmorillonite Iron talc Barium sulfate Calcium carbonate

The greatest grain size which is to be regarded as usable for application according to the invention, has turned out to be 150 μm.

Further, according to above thoughts, another table has been made which also takes into regard the heat conduc¬ tive ability of the agent. To the right in this table a "second product" has then been made by means of specific weight x specific heat x heat conductivity.

Heat cond. Temp. cond. "Second product"

(at 18°C) figure cal²/cm⁴, s, °C² calcm, s, °C cm l~

0,5 0,87 0,27

0,08 0,23 0,03

0,08 0,20 0,13

0,91 1,09 0,74

0,27 0,40 0,17 0,006 0,010 0,004

0,005 0,009 0,003 0,0014 0,005 0,0003

0,00036 0,0010 0,0001 0,0013 0,0013 0,0013

0,0004 0,0010 0,0002

As appears from the table, great variations can be found in this second product. It seems to be impossible to com¬ pensate for a long "second product figure" by decreasing the grain size. However, it seems to be necessary that this "second product" exceeds 0,002 cal²/^c:m⁴, s, °C² (= 10 x the product for castor oil) . At experiments which have been carried out, varying degrees of the content of the fillers according to the invention, have been tested to be able to investigate and compare different properties when spraying at room temperature (approx. 20°C), in accordance with the most preferred embodiment which is defined in claim 8. Very good results have been obtained with a filler degree (weight %) corresponding to 30-40 % of a filler with high heat capacity. By using such a high degree of such a filler it has been possible to cover the surfaces 2 with a protecting agent with more than 10 % thermoplastic rubber.

The following recipes show (weight %) components used and different qualitative properties for five different com¬ positions.

Recipes and qualitative properties

2 3 4 5

40 28 20 17 6 4 4 3 10 7 7 6

1 2 1 2 1 2

10 10 20 25

20 13 12 11 6 4 3 3 12 5 9

10 10 10

5 12 9

4 4 4

100 100 100 100 100 Properties of the above liquid covering composition

1 2 3 4 5

Solid content 100% 100% 100% 100% 100%

Storing ability Good Good Good Good Good Spraying ability Good Bad Good Good Good

Properties of the above cooled covering composition (layer thickness in urn)

I 2 3 4 5

Max layer thickness 1000 1000 1000 1000 1000 no flowing

Corrosion resistance Good Good Good Good Good 250 m/240H

Scab corrosion test Good Good Good Good Good 6 months

Flexibility at low Good Good Good Good Good temp f-30°C1

Wearing resistance 10-15 m 1-2 h 1-2 h 4-5 h >5 h

It is hereby shown that the recipe (2) that does not contain fillers according to the invention, has bad spraying ability. It is evident that an addition of at least 20 % of thermoplastic rubber gives a very good wea¬ ring resistance.

As an example of a thermoplastic rubber, articles can be mentioned which are sold under the trade mark Cariflex^® (Shell Chemical Company) the chemical composition of which is:

Styrene-butadiene-styrene (SBS) Styrene-isoprene-styrene (SIS) Styrene-ethylene/butylene-styrene (S-E/B-S) In the claims and the description the expression "glue- based" has been mentioned. By this expression is meant that the corrosion protection is based on a "binder" which gets its adhesive and cohesive properties after being heated and cooled. Further, the expression "high degree of wearing resistance" has been used. A high deg¬ ree of wearing resistance means that the corrosion pro¬ tection for the under part of cars, in this case hot- melt, has the ability to withstand:

1. 5 hours* testing in a stone shot test without being penetrated (Daimler-Benz method) .

2. 10 years normal driving with a car without pene- tration.

In Fig. 2 a modified method according to the invention is shown. With this method, the amount of fillers with which heat capacity can be drastically reduced by raising the surrounding temperature. Fig. 2 shows the limited space 11 in which an object 2 is located which is to be corro¬ sion-treated. Within the space 11 there is also, at least preferably, a mobile robot 21 (shown schematically) and equipped with a nozzle 14. Within the limited space 11 the application of an anticorrosive agent 15 is carried out at elevated temperature. Due to the fact that the application occurs at elevated temperature the unfavour¬ able forming of "co-webbing" is eliminated or avoided, which "co-webbing" arises at spraying of a thermoplastic rubber at normal temperature.

To be able to maintain a suitable temperature, for in¬ stance 50° C, suitable means are connected to the space 11. In the example shown, this means consists of a con- trol arrangement 18 that via a first pipe 19 supplies tempered air to the space 11 and a second pipe 20 con- ducting air out of the space. The man skilled in the art will realize that heating of the space also may be carri¬ ed out within said space in an other way, for example by means of radiators.

In Fig. 3 the object 2 and the nozzle 14 are shown as a partial view of Fig. 2. The figure shows that a robot 21 keeps and directs a nozzle 14 so that the fog 15 is ap¬ plied to the surface 13 that is to be corrosion-treated. The anticorrosive agent 15 containing thermoplastic rub¬ ber, is supplied to the nozzle 14 in a conventional way, suitably by means of existing equipment 17. This means that the mass is supplied in a melted phase at a tempera¬ ture of about 150° C and at an approximate pressure of 100 bar, (which of course can vary within known limits for the man skilled in the art) . Without surplus efforts it is, consequently, possible, by means of the invention, to have one or more robots (or possible persons) to work simultaneously.

As shown in Fig. 4 it is preferred that one wall of the space consists of the object 2 that is to be corrosion- treated. For cars it may for example be convenient to let the underside of the car be the roof of the limited space 1. It is released that more than one "wall" of the space may be made up of the object. In an extreme case it is thinkable to have all limiting surfaces made up by the object, that is a fully covering interior anticorrosion treatment.

By combining this method with an anticorrosive agent with fillers according to the invention, one can modulate the temperature or degree of admixing to be able to adapt the combination thereof to each situation. The man skilled in the art will easily realize that the invention is not limited to the above described, but can be varied within the scope of the following claims. Thus, the invention is not limited to the materials which are sold under the classification thermoplastic rubbers, but can of course be used for all kind of polymers that can be expected to have varying resistant influence on an anticorrosive agent and that has the property that they have an unfavourable change of the phases if the cooling at normal application is too large. Thermoplastic polyme¬ rs are therefore a more relevant denomination. It is also realized that the amount of the different parts can vary within relatively wide limits. One has made tests with acceptable results when the binder part has varied between 30-70 % and the part of fillers in a correspon¬ ding way varied between 65-15 %. What relates to the art of thermoplastic rubber, the man skilled in the art will realize that the wearing protection of the cover increa¬ ses with increased part of thermoplastic rubber. The part is, accordingly, proportional to desired degree of wear¬ ing protection. A content of approximately 8-12 % gives a cover with good resistance against wearing and composi¬ tions with up to 30 % thereof, which then have extremely high resistance against wearing, should be commercially acceptable. Neither the modified method is limited to the above described, but it is realized that, for example, the temperature in the space can be varied within wide limits and that, if the temperature is sufficiently high in the space, the filler with high heat capacity can be completely expelled. As already mentioned, robots are preferably used for the spraying work. How many (for ex¬ ample 2, which are shown in Fig. 3) and what kind of ro¬ bots, that should be used, is a question of adaption which is within the order of the normal development work of the man skilled in the art, and preferably in cooperatin with people in the robot field.

Claims

1. Composition intended to be applied on a surface (2) by spraying of the hot, liquid composition for ob¬ taining a cover which is resistance to wear and corrosion attacks, the composition comprising a first glue-based binder part, a second part with fillers and a third part consisting of a thermoplastic polymer containing thermo¬ plastic rubber, c h a r a c t e r i z e d in that said second part of fillers contains substances with high heat capacity.

2. Composition according to claim 1, c h a r a c ¬ t e r i z e d in that the product of the specific weight of the fillers (15°C) and the specific heat (15°C) exceeds 0.32 cal/cm³, °C, preferably 0,5 cal/cm³, °C.

3. Composition according to claim 2, c h a r a c ¬ t e r i z e d in that said second part is added in an amount of 15-65 % by weight.

4. Composition according to claim 3, c h a r a c ¬ t e r i z e d in that the mathematical product for sub¬ stances in said second part and relating to the proper¬ ties specific heat, density and heat conductivity exceeds 0,002 kal²/c°² cm⁴ s.

5. Composition according to claim 3, c h a r a c ¬ t e r i z e d in that said second part has been chosen from the group barium sulphate, iron talc, CaC0₃, talc, aluminium, copper, zink and the like.

6. Composition according to claim 4, c h a r a c ¬ t e r i z e d in that the amount of thermoplastic rubber exceeds 8 %, preferably 10 %, or in a more preferred case is within the interval of 20-25 % per weight.

7. Composition according to claim 4, c h a r a c ¬ t e r i z e d in that the binder comprises wax or bitu¬ men.

8. Method for the application of a composition ac¬ cording to claim 1, c h a r a c t e r i z e d in that it comprises the following steps:

a) heat supply (5,6) to a container (3) so that the composition (4) is kept in a liquid state at a suit¬ able temperature which is adapted for spraying,

b) activation of a pressure giving means (10) giving pressure to the composition in connection with its transport to a nozzle (7) ,

c) directing the nozzle towards the surface (2) of the object (1) that is to be corrosion-protected and thereafter an influence of an organ that initiates start of a spraying of the composition (8) towards the object (1) that is to be corrosion-protected.

9. Method according to claim 8, c h a r a c¬ t e r i z e d in that said suitable temperature is within the interval 140-200° C, and that the pressure on the composition is maintained within 50-200 bar.

10. Method according to claim 7, c h a r a c t e¬ r i z e d in that the application is carried out in an at least partly closed space (11) which keeps a tempera¬ ture which is predetermined within given limits.